Liquid chromatography pump

ABSTRACT

A fluid pump mechanism for delivering a smooth output of fluids to a system utilizing at least one piston in a chamber reciprocative therewithin. The piston has strokes that fill and empty the chamber in conjunction with the action of valve means located at the inlet and outlet of the chamber. Motive means causes reciprocation of the piston within the chamber. Control means is also included for minimizing the time during the piston cycle in which the piston is not emptying the chamber. The invention&#39;s scope also encompasses a pressure metering device for a fluid forcing means motivated by an electrical motor.

CROSS REFERENCES TO RELATED INVENTIONS

The present application is a continuation-in-part of my copendingapplication filed on Jan. 21, 1977, Ser. No. 761,433, now U.S. Pat. No.4,131,393.

BACKGROUND OF THE INVENTION

The present invention relates to a novel fluid pump mechanism which willdeliver fluid or fluids at a given flow rate and with a greatly reducedpulsation. The present invention is particularly useful, although notlimited, delivering liquid solvents at very high pressures.

For example, a typical liquid chromatographic column contains packing offinely divided particles for solute separation of a liquid sample. Thesepacked columns create a very high back pressure on the fluid forcingmeans, i.e.: a positive displacement pump. Moreover, such a pump usuallyproduces a pulsing flow due to the normal action of a piston within achamber, which can distort the analysis of the solute.

Prior devices have employed pulse dampeners on the output side of thepump as well as dual pistons with overlapping cam methods to overcomesuch problems. Flow feedback and pressure feedback pumps have been usedalso. However, these mechanisms work inefficiently and are susceptibleto breakdown because of the complexity of the components in theirmakeup. Such prior pumps still deliver pulsed flow because of chambercompliance compressibility of the fluid being pumped and other factors.

Moreover, constant speed motors driving single piston pumps will producea pulsing flow and deliver reduced flow rate at high back pressuresunless corrected. Additional components such as pressure transducers areexpensive and necessarily add to the unreliability of the liquid solventdelivery system.

There is a need for a simple, reliable, metering pump which has greatlyreduced pulsations in the delivery of fluids, especially liquidchromatographic solvents.

SUMMARY OF THE INVENTION

In accordance with the present invention a novel fluid pump mechanism isprovided.

The mechanism in its basic form includes a piston having a portionreciprocative within a chamber. Valve means permits the filling andemptying of the chamber with the corresponding strokes of the piston. Togenerate a smooth and relatively pulse free flow of fluid from themechanism, control means masters the reciprocation of the piston whenthe chamber is not in the process of emptying or delivering the fluidbeing pumped. Generally, this would externalize in a speeding up of thepiston during its filling stroke and a speeding up of the piston duringthe "pump-up" period, which is the time when the piston moves to deliverthe fluid being pumped, but before the fluid leaves the chamber. Pump-upresults from the exertion of back pressure on the chamber outlet, aswell as fluid and piston compressibility, seal compliance, and otherfactors.

Motive means such as, but not limited to an electric motor, drives thepiston through its reciprocations within the chamber at a normal or basespeed commensurate with the desired flow rate of fluid during theemptying stroke of the piston.

The control means during the filling period may include detection meansto acquire and signal the inception of the filling stroke of the piston.Such detection means may take many forms such as a light or photoninterception flag rotatable with a shaft actuating a reciprocating meanswhen the motive means includes such elements. A light or photoninterceptor module would generate such a signal. Interception of thisphoton signal would then generate an electrical signal announcing thebeginning of the piston filling stroke to filling means which wouldchange the normal speed of the motive means to a speed, usually higher,which would cause filling or refilling of the chamber as quickly aspossible. The speed of filling setting would depend on such criteria ascheck valve response and, degassing or cavitation characteristics of thefluid being pumped. Thus, the pump mechanism completes the filling orrefilling phase as quickly as possible so that the piston may devote itsgreatest effort toward pushing the fluid from the chamber.

Likewise, the detection means may be constructed along the lines of adigital counter having a pulsing tachometer measuring the turning of themotive means shaft. A digital counter would sum these pulses from thepulsing tachometer during the filling period and effect the change ofspeed of the motive means and piston. Further, the analog equivalent ofthis digital integration, i.e.: analog integration, may perform the samefunction.

Where the motive means has reciprocating means, such a format mayinclude a cam shaft, linked to the shaft of the motive means; camsurface; and a cam follower connected to one end of the piston. Thedetection means would be coordinated with the corresponding portions ofthe piston cycle devoted the filling of the chamber. After filling, thepiston returns to pump the fluid from the newly filled chamber but theflow of fluid delays for a number of reasons. For instance, the backpressure of the body to which the fluid is being pumped, will permit thevalve means on the outlet check valve to open only when the backpressure is equaled by the fluid pressure within the chamber. This"pump-up" portion of the cycle also depends on fluid compressibility,seal compliance, and piston and chamber compliance. Under mostconditions, the pump-on portion of the piston cycle extends for a finitetime during which no fluid passes from the chamber. The mechanism alsoembraces pump-on means to increase the speed of the motive meansimmediately after the termination of the chamber filling stroke of thepiston and returns the motive means to a predetermined normal speed whenthe chamber reaches the proper pressure to open the valve means on thechamber outlet. The pump-up means may be mated with the fast filling orfast refilling cycle of the piston heretofore described.

In one aspect, the pump-up means may include a running or variablesystem to fix the increased speed of the motive means according to thevalve of the back pressure encountered. For example, pressure signalmeans would acquire and transmit the valve of the back pressure tocomparitor means. Pump-up gain means would produce a selected referenceramp signal to the comparitor which would step up the motive means foran angular duration ie: a certain number or fraction of turns of themotor shaft. The pump-up gain means might include tachometer means formeasuring the axial rotational rate of the motor shaft and transformingthe same into a pulse signal. Gain means would receive the puls signaland adjust its amplitude to a certain value. Charge integrator meansintegrates the amplitude adjusted signal from the gain means andproduces a reference ramp signal proportional to the motive meansangular duration.

The invention also devises a novel means for deducing the pressure onthe motive means if it is an electric motor actuating a fluid forcingmeans for displacing the fluid against a back pressure. Pressuremeasuring means tarnsforms the torque load measured on the electricalmotor to a valve of pressure for the fluid forcing means. In the case ofa shunt wound or permanent magnet D.C. motor the torque load is measuredin terms of a current supplied to the motor.

The pressure signal means associated with the pump-up means may be oftorque load type. Likewise, the pressure signal means may indicate thepressure of the system only while the fluid pumps out from the chamberand not during filling or pump-up. The pressure determined from themotor's torque load may be fed to a readout as well as to means fordeactivating the electrical motor at a preselected high and/or low valueof pressure. Blanking means may be included to interrupt the pressuremeasuring means during a portion of the piston cycle e.g.: filling andpump-up.

Thus, a novel and useful pump mechanism has been invented whichminimizes the time duration of filling and pump-up of a pumping pistonand maximizes the time duration of fluid flow at high pressures with aminimum pulsation.

It is therefore an object of the present invention to provide a lowcost, reliable, and efficient pump mechanism for delivering fluids athigh pressures in a pulseless state.

It is another object of the present invention to provide a pumpmechanism compatible with liquid chromatographic systems including butnot limited to packed columns.

It is yet another object of the present invention to provide a pumpmechanism which will increase the time during which fluid is deliveredto a receiving system and decreases the time of filling or refilling andpump-up prior to such delivery.

Another object of the present invention is to provide a pump mechanismwhich meters fluid flow under high pressures.

Still another object of the present invention is to provide a pumpmechanism which measures pressure from the troque load on its motivemeans and feeds this value back to the motive means as a method ofmotive means speed control.

Another object of the present invention is to provide pressure signalmeans for an electric motor in combination with fluid forcing means interms of the measurement of torque load on such an electric motor.

The invention possesses other objects and advantages especially asconcerns particular features and characteristics thereof which willbecome apparent as the specification continues.

Various aspects of the present invention will evolve from the followingdetailed description of the preferred embodiment thereof which should betaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of the mechanism with the piston section shownin section.

FIG. 2 is a view taken along line 2--2 of FIG. 1.

FIG. 3 is a view taken along line 3--3 of FIG. 1.

FIG. 4 is a view taken along line 4--4 of FIG. 1.

FIG. 5 is a broken side view of the tachometer section shown in FIG. 4.

FIG. 6 is a block diagram of the electrical control means.

FIG. 7 is an electrical schematic diagram of a preferred embodiment ofthe invention.

FIG. 8 is a block diagram of a preferred embodiment of the invention.

FIG. 9 is a block diagram of a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pump mechanism of the present invention as a whole is indicated inthe drawings by reference character 10 and includes as one of itselements a piston 12 which reciprocates within chamber 14. Piston firstend portion 16 contacts the fluid traveling into and out of chamber 14,and piston second end portion 18 contacts motive means 20. Piston 12moves back and forth within chamber 14 to fill and empty the chamber offluid. As depicted in FIG. 1, the chamber fills when piston 12 movesfrom right to left.

Chamber housing 22 includes set screws 24 and studs 26 which engage pumpbody 28 to hold the chamber housing 22 in place. Plunger 30 rides withinplunger barrel 32 and on bearing 33, and connects to piston second endportion 18 via ferrule 34. Seal 36 maintains the pressure integrity ofchamber 14. Valve means 38, FIG. 2, includes an inlet check valve 40 andan outlet check valve 42 which threadingly engage chamber housing 22.Opening 44 permits the removal and inspection or repair of theconnection of piston 12 to ferrule 34.

Plunger 30 terminates at the end opposite to piston second end portion18 in a cam follower 46 which rolls or slides on cam surface 48 of cam50. Cam support 74 further stabilizes cam follower 46. Spring means 52bears on collar 54 of plunger 30 and shoulder 56 of pump body 28. Plate58 and connecting bolts 60 permit access to the cam 50. Motive meansfurther includes cam shaft 62 which turns by dint of the rotationalforce of electric motor 64, FIG. 1. The cam shaft 62 turns hub 66,within bearing 68 and seals 70, which in turn connects to hub 72 holdingcam 50. Cam shaft 62 is reduced, by any conventinal means, to a slowerspeed, on the order of 50:1, than shaft 73 which turns without reductionon the opposite side of electric motor 64.

Control means 76, including detection means 77, shown in block diagramFIG. 6, interfaces with the mechanical elements of FIGS. 1 and 2 with adetector 75 such as photon intercepting flag 78 which turns with camshaft 62 on hub 66, FIG. 3. Detector 75 further includes photonintercepting module 80 which fastens to motor housing 82 by means ofbracket 84 and set screws 86. Terminals 88 relay the photon interruptionof flag 78 to filling means 79. Similarly, shaft 73 terminates intachometer means 90, FIGS. 1, 4, and 5, which has a graduated wheel 92and an optical detector 94. The wheel 92 is graduated into 360transitions one for each degree of turn. Again terminals 88 transmit thelight interruption in a series of electrical pulses. Disc 98 holdsgraduated wheel 92 onto shaft 74 with the aid of friction wheel 100.Optical detector 94 is supported by bracket 102 and set screws 104 inplace. Appendage 106, fixed to motor housing 82 supports brackets 84,and 102 as desired.

Control means 76, FIG. 6 changes the speed of motive means 20 during thetime period other than the time period when the chamber 14 is beingemptied of fluid.

Turning to the block diagram, FIG. 6, normal or constant speed settingmeans 108 directs voltage to current sink converter 110 to pull acurrent proportional to constant speed setting means 108. Summing node116 measures the error current between the current determined by theconstant speed setting means 108 and the current from frequency chargepump 118 which produces a current proportional to the speed of motivemeans 20 measured by tachometer means 90. Summing amplifier 120, a highgain amplifier, delivers a servo error signal according to referencevoltage 122 in comparison with the instantaneous error current atsumming node 116. Servo gain and compensation means 124 providesfeedback to summing node 116, but is a relatively small current whencompared to the current from frequency charge pump 118.

Pulse width modulator generator driver 126 generates pulse widthmodulated signal which has a duty cycle proportional to the input errorsignal from summing amplifier 120. Pulse width modulator generatordriver 126 then provides a changing voltage to motive means 20, whichmay be a D.C. motor. Thus, constant speed setting means 108 determinedthe speed of motive means 20 through a null circuit, including summingnode 116, servogain and compensation means 124, summing amplifier 120,and reference voltage 122, and pulse width modulator generator driver126.

After delivery of the fluid in chamber 14 by the emptying action ofpiston 12, at a selected normal or substantially constant speed,detection means 77 will acquire and signal the inception of the fillingor refilling stroke of piston 12, and signal the termination of suchfilling stroke. As previously discussed, such detection means 77 may beaccomplished in the preferred embodiment by a photon intercepting flag78 interrupting module 80, during the filling stroke of piston 12.Likewise, detection means 77 may take the form of a pulsing tachometercoupled with a triggered or resetting digital counter to sum pulsestherefrom, to indicate the period of the filling stroke of piston 12.For example, in the present embodiment, the onset of the filling ofchamber 14, where motive means 20 includes a D.C. motor, reverses theload upon such motor because of the negative slope 51 on cam 50. Thesudden drop in motor current may be detected and employed to start adigital counter. This indication of the beginning of filling stroke ofpiston 12 may be accomplished by other timing or shaft rotationalmeasuring devices known to persons of ordinary skill in this art. Thedigital counter would determine the angular duration of the fillingperiod. An analog integrator could also be employed for this purpose, byintegrating a tachometer signal and producing an output proportional toangular duration for the filling period. The digital count would becompared to a standard count representing the filling movement of piston12. The analog integrator, on the other hand, would be compared to afixed or reference voltage representing the end of the piston's fillingstroke. A typical value of the angular duration of the filling orrefilling stroke of piston 12 is about 50 degrees.

Filling amplifier 128 coupled to a detector 75 senses the beginning ofthe filling stroke of piston 12 and signals and activates first switchmeans 114 via "OR" gate 130 and second switch means 132 directly. Firstswitch means 114 in conjunction with constant speed decoupling means 112effectively bypasses the voltage to current sink converter 110 andpump-up speed control 152 from summing node 116. Thus, filling speedcontrol means 134 determines the speed of motive means 20 while thepiston 12 moves through its filling or refilling stroke. Filling speedcontrol means 134 increases the speed of motive means 20 in most casesat a rate commensurate with such considerations as, the cavitation anddegassing characteristics of the fluid, liquid, solvent, or the like,being pumped by mechanism 10.

Furthermore, the speed of valve means 38, as well as the hydraulicgeometry of the mechanism 10 must be considered as a limiting factor forpumped liquids. At very fast normal speeds, the motive means may slowduring filling because of these factors. This is especially true of lowboiling point solvents such as pentane, ethyl ether and the like.

The inception of filling speed-up by filling means 79 also sets chargeintegrator 136 to a very low value and it remains there during therefilling stroke of piston 12. The termination of the refilling strokeof piston, 12 signaled by detection means 77, deactivates switch means114 and 132. However, fluid is not delivered until the emptying strokeof piston 12 overcomes the back pressure on outlet check valve 42 andpiston seal compressibility, liquid compressibility, chamber deformationand like phenomena, generally referred to as "compliance". For a typicalliquid chromatographic system piston 12 must travel along its emptyingstrokes approximately seven (7) micro-liters for a 140 kilogram/squarecentimeter back pressure, with a generally linear increase thereafter.This period in piston 12's reciprocations is called "pump-up".

At the beginning of pump-up, pump-up means 138 changes the speed ofmotive means 20. Pump-up means encompasses pump-up gain means 142 whichincludes tachometer means 90 measuring the axial rotational rate ofshaft 73 and transforming this measurement of axial rotation into apulse signal received by frequency charge pump 118. Gain means 144 whichmay be coupled with frequency charge pump 118 adjusts the amplitude ofthe pulse signal from the tachometer means 90 or the frequency chargepump 118 and transmits the amplitude adjusted pulse signal to chargeintegrator 136. A ramp signal results which feeds into comparitor means140. Such a ramp signal is proportional to shaft 73 rotation, cam 50rotation or the linear displacement of piston 12.

Comparitor means 140 utilizes comparitor 146 which also receives a backpressure signal from pressure measuring means 148. The output ofcomparitor 146 travels through "and" gate 150 while the chargeintegrator 136 output increases but is less than the back pressuresignal, i.e.: during the pump-up period. The comparitor 146 outputs addsan additional current to ground from summing node 116 via pump-up speedcontrol means 152. The "step-up" of pump-up speed control increases thespeed of motive means 20 until the ramp signal substantially equals theback pressure measuring from pressure signal means 148. This, of course,means that the piston 12 has generated enough fluid pressure to overcomethe back pressure on outlet check valve 42, provided that gain means 144has been properly adjusted, and the pump mechanism 10 reverts to itsnormal or constant filling speed. Integrator 136 stays high until thenext refilling cycle. There is essentially an instantaneous switch fromfilling speed change to pump-up speed change to minimize or eliminateany slack when fluid is not being delivered. Pump-up speed controlisolator 154 prevents activation of pump-up speed control during normaloperation.

Pump-up gain means 142 may increase or decrease the pump-up periodmeasured in piston linear displacement or in the angular rotation of theshaft 73 for a given back pressure signal. Gain means 144 specificallyincreases or decreases the slope of the ramp signal to this end.Changing the pump-up period is necessary to correct for different liquidsolvent viscosities, chromatographic column resistance and other factorsaffecting flow rate.

Since the time span of filling and pump-up are finite, the desired flowrate determined at the normal speed setting means 108 may not equal theactual average flow rate from the outlet of chamber 14. Thus "pump-up"may exceed the time when outlet check valve 42 opens in some cases.Also, the back pressure on check valve 42 may drop during filling and"pump-up" producing a slight pulse in the fluid flow. Gain means 144also reduces this pulse by matching the flow rate setting with theacutal flow rate delivered by mechanism 10.

The preferred embodiment is deemed to be drawn to a pressure signaldevice alone or in combination with the heretofore described pumpmechanism 10. Pressure measuring means 148 measured the torque on motivemeans 20 and transforms the same into a measurement of back pressureassociated with a fluid forcing means such as piston 12 and chamber 14.Motive means 20 may include a direct current electric motor in whichcase, the current delivered to the motor would be proportional to thetorque load on the motor and therefore would be transformable into ameasurement of back pressure by pressure measuring means 148.

Means 158 for deactivating the motive means 20 at selected back pressurevalves, either high or low or both, may take the form of a high lowpressure detector 160 with a limit indicator 162. High pressure limitingmeans 164 may be provided with hysteresis means 164 for reactivating themotive means 20 when the back pressure again falls within the selectedworking range.

Drive detector means 168 and time delay means 170 as well as comparitoroutput 146 through inverter 172 and "and" gate 150 feed to "and" gate174. The output of "and" gate 174 and the output of high low pressuredetector 160 travel through "or" gate 176 and inverter 178 to deactivatepressure measuring means, and form blanking means 180. This prevents themeasurement of pressure during filling, pump-up and a coasting downperiod after pump-up for a set time period, provided by time delay means170.

Block diagram, FIG. 8, shows a variation of the invention 10, inparticular, control means 76. Detection means 77 could signal theinception of the chamber filling stroke of piston 12 and may take theform of the photon interruption flag 78 and associated elements andother equipment structures previously described. However, detectionmeans 77 is shown as signaling the inception of the pump out of fluidduring the normal pumping period of piston 12. At this time switch means182 is "on" and switch means 184 is "off". Switch means 182 and 184 maytake the form of analog transmission gates. At this point, the torqueload on motive means 20 is constant and proportional to the backpressure of the liquid being pumped. Normal or constant speed settingmeans 108, previously delineated, determines the speed of motive means20 via servo summing amplifier 186 which produces an amplified errorsignal from the tachometer 90 and normal speed setting means 108 inputs.

During normal flow, a negative feedback loop 187, consisting of summingamplifier 188, integrator 190 and switch means 182, produces an averagetorque error signal at node 192 of zero. Summing amplifier 188 comparesthe instantaneous motor current from sensing resistor R-25, which isproportional to torque when motive means 20 in a D.C. motor, to theoutput of integrator 190. Integrator 190, in turn, receives the torqueerror signal of the negative feedback loop 187 and an input from ground.

In other words, the output signal of integrator 190 equals the averagesignal across the current sensing resistor R-25, during normal pumping.

At the inception of the filling period detection means 77 cause switchmeans 182 to turn "off" breaking the negative feedback loop 187, andfreezing the output of integrator 190, to its last value. Switch means184 is turned "on" via inverter 185. During filling, the torque onmotive means 20 greatly reduces such that the torque signal input tosumming amplifier 188 is less than the output signal of integrator 190.The torque error signal i.e.: summing amplifier 188 output, travelsthrough switch means 184 to servo summing amplifier 186. The addition ofthe torque error signal, thereto, will cause motive means 20 to run atmaximum speed because of the large amplified error signal received fromservo summing amplifier 186.

At the end of refill, and the beginning of pump-up, the load on motivemeans 20 increases and the torque error signal begins to drop. As theload continues to increase the torque error signal further decreasesuntil motive means 20 begins to decrease. By the end of the pump-upperiod, the torque error signal decreases to zero and has no furthereffect on servo summing amplifier 186. Therefore, motive means 20returns to the normal speed for pumping the fluid. Detection means 77again signals the inception of the normal pumping period which turnsswitch means 184 "off" and switch means 182 "on".

Differentiator 194 produces a signal proportional to the acceleration ofmotive means 20. This acceleration signal is subtracted from the torquesignal of R-25. The net result is a true torque error signal to servoamplifier 186 during filling and pump-up. As may be surmized theembodiment of FIG. 8 does not require a compressibility adjustmentnecessitating gain means 144 in the prior embodiment.

FIG. 9 depicts another embodiment of the present invention where theactual pressure in the piston chamber 14 is sensed by a pressuretransducer 196 instead of using motor torque as the pressure sensor. Thenull loop 187 formed by summing amplifier 188 and integrator 190 tracksthe piston chamber pressure when switch 182 is "on". Switch 182 turns"on" by the action of sensor 77 during the guaranteed delivery stroke ofpiston 12, that is to say, after the pump-up period. Thus, theguaranteed delivery period necessarily excludes the initial period ofthe piston's forward stroke which produces pressure to overcome the backpressure on the system. The guaranteed delivery period would exclude,therefore, sufficient piston displacement to allow pressurization ofchamber 14 to the highest operating pressure of the pump i.e.: 6,000 to10,000 P.S.I.

Switches 182 and 184 are driven out of phase. When switch 182 is on, theaction of null loop tends to minimize or zero-out signal 192. Nullcircuit 187 servos to the average value of pressure signal 198, sinceamplifier 188 defines the difference between the actual chamber pressuresignal 198, and the output of integrator 190 and the null loop 187defines the average difference to be zero. When switch 182 turns off(during refill and pump-up) there is no input to the integrator 190.Output of integrator 190 remains unchanged in a hold state. At thistime, output of integrator 190 is equal to the previous average pistonchamber pressure during the delivery stroke.

A velocity servo control loop consisting of summing amplifier 186,setting means 108, motive means 20 and tachometer means 90 regulates thespeed of motive means 20 to whatever value is set into normal speedsetting means 108. The configuration of cam 50 insures a metered flowrate of fluid from chamber 14 during the delivery stroke of piston 12.

At the end of the delivery stroke of piston 12 detection means 77 opensswitch 182 which holds the average pressure signal, i.e. the output ofintegrator 190. Switch 184 closes which connects the pressure errorsignal 192 to the servo summing amplifier 186. During refill and pump-uppressure error 192 is large and negative. Pressure error signal 192feeds into a negative input on servo summing amplifier 186. Thisnegative error signal increases the speed of motive means 20 to overcomethe pressure error. As a net result, refill and repressurization occurin the minimum possible time, dependent on the maximum attainable speedof motive means 20. Pressure error signal 192 approaches zero when thepiston chamber pressure equals the previously remembered value. Thisallows the velocity of motive means 20 to return to its normal speedand, assure the correct flow rate therefrom, as defined by normal speedsetting means 108. By this embodiment, the time during which piston 12is not delivering is minimized. Flow rate is concurrently corrected forsolvent and system compressibility. Thus, the need for a compressibilitycompensation adjustment is eliminated. Although short duration pulsesensue they are easily filtered on the outlet of the pump chamber 14, bya hydraulic pressure filter, well known in the art.

Now considering the schematic circuit drawing FIG. 7 the following TableI is a list of the elements found in the circuit with the model numberof values used in the embodiment shown in FIG. 6.

                  TABLE I                                                         ______________________________________                                        TABLE OF ELEMENTS                                                             ______________________________________                                        INTEGRATED CIRCUITS                                                           Z - 1 National Semi-conductor LM 2907N                                        Z - 2 National Semi-conductor LM 339N                                         Z - 3 National Semi-conductor LM 324N                                         Z - 4 R.C.A. CD 4066 AE (QUAD BILATERAL SWITCH)                               DIODES                                                                        CR 3 through CR 17,                                                           CR 22, CR 23, CR 24                                                                         IN 914                                                          CR 18, CR 19  MR 850                                                          TRANSISTORS                                                                   Q - 3, Q - 4  2N 930                                                          Q - 11        2N 5189                                                         Q - 9, Q - 10 MPS 3638A                                                       Q - 1, Q - 8, Q - 7,                                                                        MPS 6531                                                        Q - 13        R.C.A. 2N6386                                                   Q - 2, Q - 5, Q - 6                                                                         M.P.S. 4355                                                     Q - 12        R.C.A. 40375                                                    CAPACITORS                                                                    C - 16, C - 19                                                                              15 uf, 20 v                                                     C - 4, C - 9, C - 12,                                                                       0.1 uf, 50 v                                                    C - 17, C - 18                                                                C - 5         0.02 uf, 100 v (± 20%)                                       C - 6, C - 13 2.2 uf 50 v (ceramic)                                           C - 7         C20 Pf ± 2.5%                                                C - 8         0.001 uf ± 20%                                               C - 11        100 uf, 50 v (electrolytic).                                    C - 14        1.0 uf                                                          C - 15        0.01 uf                                                         RESISTORS                                                                     R - 25, R - 27                                                                              0.3 ohms, 2 w                                                   R - 26        68 ohms, 2 w                                                    R - 20        47 ohms, 1/4 w                                                  R - 22        68 ohms, 1/4 w                                                  R - 17        470 ohms, 1/4 w                                                 R - 2, R - 21, R - 45,                                                                      1 Kohm, 1/4w                                                    R - 73                                                                        R - 28, R - 18                                                                              1.5 Kohm, 1/4 w                                                 R - 5, R - 14 2.2 Kohms, 1/4 w                                                R - 29, R - 43                                                                              3.3 Kohms, 1/4 w                                                R - 16        3.9 Kohms, 1.4 w                                                R - 9, R - 41, R - 49                                                                       4.7 Kohms, 1/4 w                                                R - 13, R - 33, R - 38,                                                                     10 Kohms, 1/4 w                                                 R - 52, R - 54, R - 65,                                                       R - 68, R - 69                                                                R - 51, R - 53                                                                              15 Kohms, 1/4 w                                                 R - 12, R - 4, R - 67                                                                       22 Kohms, 1/4 w                                                 R - 11, R - 44, R - 48,                                                                     30 Kohms, 1/4 w                                                 R - 74.                                                                       R - 10, R - 30                                                                              39 Kohms, 1/4  w                                                R - 15, R - 46                                                                              47 Kohms, 1/4 w                                                 R - 64, R - 8, R - 34,                                                                      100 Kohms, 1/4 w                                                R - 70, R - 72                                                                R - 31        120 Kohms, 1/4 w                                                R - 14        200 Kohms, 1/4 w                                                R - 39, R - 40                                                                              220 Kohms, 1/4 w                                                R - 35        150 Kohms, 1/4 w                                                R - 42        390 Kohms, 1/4 w                                                R - 47        420 Kohms, 1/4 w                                                R - 7, R - 6, R - 71                                                                        10 Mohms, 1/4 w                                                 R - 37        7.5 Kohms, 1/4 w                                                R - 58        499 Kohms, 1/4 w                                                R - 59        12.1 Kohms, 1/4 w                                               R - 57        42.4 Kohms, 1/4 w                                               R - 56        27 Mohms, 1/4 w                                                 R - 3         560 ohms, 1/2 w                                                 R - 41        4.7 Mohms, 1/4 w                                                R - 32, R - 55, R - 60                                                                      10 Kohms, (trimpot)                                             R - 36        100 Kohms, (trimpot)                                            R - 50        10 Kohms, (trimpot)                                             R - 66        75 Kohms, 1/4 w                                                 R - 101       10K, ratio 100/10.0 (Digital                                                  Potentiometer)                                                  R - 102       10 Kohms                                                        R - 103       10 Kohms.                                                       MISCELLANEOUS                                                                 OD - 1, OD - 2                                                                              Optical Detector - G.E.                                                       photon coupled interrupter                                                    Module # 13A1                                                   T - 1         Thermister 250 Kohms at 25° C.,                                        50 Kohms at 70° C.                                       S - 1         Electrical motor, permanent                                                   magnet motor, 1/30 H.P., 12 v D.C.,                                           amps. 0-3000 RPMS, 50:1 gear ratio.                             M - 1         Meter, 0-1 milli amps (full scale)                              I - 102       Light emitting diode #HP5082 - 4940 -                                         44403                                                           SW - 1        Single pole single throw, slider                                              switch.                                                         L - 2         300 U Henry, 3 amps.                                            ______________________________________                                    

The power inputs are denoted by a small circle with the approximatevoltage value in the vicinity of the power input, in volts D.C.

Normal speed setting means 108 may take the specific embodiment shownwhere R-101, a variable resistor combines with R-58 and C-14 which actas a low pass filter that averages the alternating current variationsfrom a direct current signal ie: a pulse width modulated signal. This isespecially true when the signal comes from a remote programer not shown.R-55, R-56, R-6, and R-57 inject a zero offset to normal speed settingmeans 108. Therefore, the R-55 zero setting becomes a true zero.

Voltage to current sink converter 110 corresponds to operationalamplifier Z-3-b in whose outputs enter Q-4, a high gain transistor.Q-4's collector pulls current through R-59 and R-60 to match the inputsto amplifier Z-3-b. It should be noted R-60 is a variable resistor whichmay be used as a calibration control for the voltage to current sinkconverter. R-61 and CR-7 combine to correct for non-linearity of thenormal speed setting means 108 and its flow rate determination becauseof the rilling means 79. This is especially useful at low flow rateswhere the distortion is greatest.

R-65 serves as the normal speed decoupling means 112. It has equalvoltage on the order of 7.5 volts on either side for decoupling normalspeed setting means 108 and pump-up means 138 when Z-4-b, which is firstswitch means 114, is turned "on" by filling means 79.

The summing node 116 leads directly into Z-1 which corresponds tofrequency charge pump 118, a frequency to current converter withfrequency doubling characteristics. Z-1 also includes summing amplifier120, a high gain amplifier.

Tachometer means 90, OD-1, sends to Z-1, a pulsating current whosefrequency is proportional to the speed of motive means 20. R-4 serves asa pull-up load resistor while C-4 acts as a decoupling capacitor toblock the D.C. component of the A.C. signal coming from the choppingaction of OD-1. The A.C. signal passes to Z-1 and is referenced toground through R-67. C-7 determines the quantity of charge delivered,for each axis crossing of the A.C. signal, by the frequency charge pump118; hence C-7 determines the gain of the charge pump. R-9 is apull-down resistor from the output of the summing amplifier 120 withinZ-1.

Frequency charge pump 118 passes current from Z-1 to R-53 and finally tosumming node 116. Likewise, the output of summing amplifier 120 with theaid of pulldown resistor R-9 produces a very small negative feedbackcurrent through R-7 to summing node 116. CR 3, and CR 4 are used forclamping limits on the error signal at the summing node 116. In thiscase, the output of the summing amplifier 120 and summing node 116 cannot go below 7 volts. Thus the recovery time of the summing amplifier120 is reduced if it becomes overloaded.

C-5, R-8, and C-6 determine the high frequency gain rolloffcharacteristics. ie: the values have been predetermined such that thewhole servo loop does not oscillate and has proper dampingcharacteristics as well as maximum response time R-5 provides a pull-upcurrent to a portion of the summing amplifier 120 within Z-1. R-6injects a small positive current into summing node 116 which adjustsR-55 to a true zero value, as previously discussed.

Summing amplifier 120 also feeds Z-2-C which comprises a part of thegenerator section of pulse width modulator generator driver 126. Theerror signal from summing amplifier 120 in Z-1 is compared to atriangular wave signal from the triangular wave from the generatorcomposed of Z-2-b, in conjunction with passive components C-8, R-11,R-13, R-10, R-12, and CR 5. The resulting output of Z-2-C is a pulsewidth modulated signal which passes to the driver section of generatordrive 126. The duty cycle of the pulse width modulated signal isdirectly proportional to the error signal from amplifier 120.

Q-8, Q-9, Q-10 and Q-11 drive Q-12 "on" and "off" synchronously at avery fast rate. R-19 is a pull-up resistor for Z-2-C while C-19 filtersthe power supplied, thereto. R-20 functions to limit the peak currentthrough Q-8. When Q-8 goes "on", Q-9 turns "off", thus Q-8 and Q-9 arecomplimentary. The pulse width modulated signal, having a frequency ofabout 25 Kilohertz, is initially high and positive, flowing currentthrough CR-15, and C-9, R-21, R-22, Q-10, and to the base of Q-11.

Q-10 bypass to ground, through CR-16, any excess current exceedingapproximately 10 milliamperes coming from Q-8. The current through R-22,the portion not bypassed, passes to the base of Q-11 turning it off. Thelimiting action of Q-10 prevents Q-11 from being overdriven on initialturn on, allowing it to turn off more quickly. After the charge-up ofC-9, R-21 limits the drive current through Q-8 to approximately 10milliamperes such that Q-10 bypasses essentially no current to groundafter the charge up period of C-9, Q-12 turns on within a time period of200 nanoseconds from the beginning of the turn on sequence causing thevoltage on its collector to reach a low value. When the pulse widthmodulated signal goes low, Q-9 turns "on" and Q-8 turns "off" allowingthe voltage at the emitter of Q-9 (top of C-9) to go low. C-9 supplies asource of negative bias in order to sink large currents very rapidlyfrom the bases of Q-11 and Q-12 through CR-17. This turns Q-11 and Q-12"off" very rapidly permitting the voltage on the collectors of Q-11 andQ-12 to go high. This "on"-"off", high/low sequence takes place at arelatively high frequency of 25 kilohertz which eliminates any audiosounds eminating from motive means 20. The need of a large heat sink todissipate heat from Q-12 is eliminated because of high/low switchingwhich takes place in 200 nanoseconds, as heretofore described.

The embodiment described also performs current limiting through Q-12using current sensing resistor R-27 and Z-2-d and its associatedcircuiting. Z-2-d is a comparitor which compares a reference voltage,established by R-14, R-15, and R-16, and a signal voltage developedacross C-15. Such a signal voltage averages the voltage drop across thecurrent sensing resistor R-27, with a weighted dual time constantoriginating from R-17, R-18, and CR-12. For instance, when the voltagedrop across R-27 exceeds the voltage across C-15, CR-12 is forwardbiased so that R-17 determines the time constant with C-15. A typicalvalue would be 4.7 microseconds in this case. On the other hand, whenthe voltage drop across R-27 is less than the voltage across C-15, CR-12is reversed biased so that R-17 and R-18 determines the time constantwith C-15 e.g.: 20 microseconds. When the signal voltage exceeds thereference voltage in comparitor Z-2-d, the output of comparitor Z-2-doverrides the pulse width modulated signal from Z-2-c, thereby shuttingdown the driver section of 126. R-15 drops the reference voltage to alow level which guarantees the driver wall remain "off" for about 30microseconds. When the signal from C-15 is discharged below the loweredreference signal, Z-2-c is re-enabled to reactivate the driver sectionof 126. The "on-off" action of this current limiting occurs at anultrasonic frequency of about 25 kilohertz again, preventing disturbingsympathetic sonic frequencies from arising. Current limiting may occurat a value of about 4 amps measured through R-27.

L-2 and C 11, a low pass filter, react slowly to current changes fromthe driver section of 126, and thereby convert the pulse width modulatedsignal therefrom to a D.C. signal supplied to S-1. R-26, Q-13, and CR 19form a dynamic break to prevent overspeeding of S-1. In other words,when CR 19 is forward biased Q-13 is "off" and the L-2 and C-11combination runs S-1. In other words, when CR 19 is forward biased, Q-13is "off" and the L-2 and C-11 combination runs S-1. However, if the D.C.voltage generated by motor S-1 exceeds the D.C. supplied across C-11,CR-19 will reverse bias and Q-13 goes "on" thereby short circuiting andbraking S-1. The CR 18 diode clamps the voltage on the collectors ofQ-11 and Q-12 to the 35 volt source when Q-12 is turned off.

Pressure measuring means 148 employs current sensing resistor R-25 whicheffectively measures the current load on S-1. This current load isproportional to the torque load on S-1 which is proportional to the backpressure exerted on mechanism 10, which may include fluid forcing meansas previously described in FIGS. 1 and 2. A motor current sensing commonemitter amplifier is embodied by Q-6 and accompanying resistors R-28,R-30, R-32, and R-33. Q-7 and R-31 form a current biasing network forQ-6. C-17 and R-29 filter high frequency noise from the currentamplification at this point.

T-1 reduces the gain of the pressur sensing amplifier Q-6, as the torqueconstant of S-1 decreases with increased temperature.

R-30 serves to limit the potential across the R-32 pot to 15 volts,consequently R-32 serves as a span adjustment for meter M-1, which willbe hereinafter discussed.

Signal conditioning of the signal from R-32 is provided by low passfilter R-34, R-70, and C-16. This R-C element may have a time constantof about 3 seconds. Z-4-D is a switch that maintains the charge on C-16when in the "off" position. The charge on C-16 represents the averagevoltage at R-32 i.e.: the output of the motor current sense amplifierZ-3-d is a non-inverting unity gain amplifier which subtracts anadjustable offset due to R-36. The output of Z-3-d equals zero volts, bythe adjustment of R-36; no back pressure is found on piston 12 at thispoint. Meter M-1 and R-37 provide a pressure readout.

Switch Z-4-d will turn off during filling, pump-up, and a time periodfollowing pump-up where the piston coasts down to a normal speed. Thisaspect of the invention shown of FIG. 6 as blanking means will be fullyexplained hereafter.

High/low pressure detector 160 includes an upper limit voltage settingmeans R-102 and a lower limit voltage setting means R-103. Z-3-Ccompares the upper limit to lower limit through resistors R-39, R-40,R-41 and R-42, CR-13 and CR 14 are forward biased between upper limitpot R-102 and lower limit pot R-103. The output of Z-3-C remains lowwhen the upper limit input is greater than the lower limit input, andthe pressure voltage at the Z-3-d output is within such limits. When theoutput of Z-3-d exceeds the upper limit, CR 13 reverse biases causingthe output of Z-3-C to go high, activating first switching means 114.R-65 becomes shorted stopping motive means 20. When the pressure on thesystem reduces, R-38, R-40, R-41 and R-42, comprising hysteresis meansof high pressure limiting means 164, restart motive means 20. When theoutput of Z-3-d goes below limit voltage, CR 14 reverse biaser causingZ-3-c output to go high shutting off motor S-1. R-103 is then adjustedto restart motor S-1. Limit indicator 16 is formed by R-43 and lightemitting diode I-102.

Filling means 79 includes detection means 77, which encompasses photonintercepting flag 78 and module 80. OD-2 represents flag 78 and module80. Z-3-A and R-47, a noise suppressor, would function as filingamplifier 128. SW-1 is a switch to disable detection means 77. Thegenerated signal from OD-2 in conjunction with filling amplifier 128turns on Z-4-B, first switching means 114, through CR 10 and R-44 whichcompose "OR" gate 130. Thus, R-66 determines the speed of S-1 duringfilling, since R-65 has equal potential on either side. Also, the outputof Z-3-A enters Q-1, through current limiting resistor R-48, which setsC-13 to a low value (i.e.: zero). C-13 would be an embodiment of chargeintegrator 136. The output of Z-3-A controls Z-4-C, which is turned "on"by the flag 78 intercepting the photon beam in module 80. Z-4-C andZ-2-A serve as "and" gate 150 and inverter 172. CR 22 and R-73 form"and" gate 174. CR 23 and R-74 comprise "OR" gate 176 and inverter 178.R-54 is a passive pull-up resistor to maintain a positive voltage onZ-4-C when Z-2-A and Z-4-C are off. Thus, a blanking signal to Z-4-Dresults during fast refill, deactivating pressure measuring means 148,as previously discussed. When such a blanking signal is received byZ-4-D holding means, C-16 will hold the value of the current senseamplifier previously described in conjunction with Q-6 at R-32. Theresult will be a steady pressure reading on pressure measuring means 148during the refill and pump-up period of the cycle of piston 12.

As soon as the flag 78 signals the end of the filling period, pump-upwill begin. A ramp signal will be produced and sent to Z-2-A whichcorresponds to comparitor 146. A second signal from Z-3-D indicates theback pressure on the mechanism 10. The advent of pump-up removes R-66from motor speed determination and substitutes the R-64 and R-65combination. In other words, the preferred embodiment adds a step to thenormal speed setting during pump-up. Also, Z-4-D receives anotherblanking signal via CR 22, and reacts as during the filling sequence.After pump-up has been completed C-18 will continue the blanking signalfor a set time period to prevent pressure measurement during the"coasting down" of motor S-1 to the normal speed setting and normal flowrate delivery.

The ramp signal arriving at Z-2-A is generated by Q-2 and Q-3 andresistors R-49, R-50, and R-52, which form a current mirror that tracksthe current flow from the Z-1 frequency charge pump, flowing throughR-53. These combined elements form pump-up gain means 142. R-50corresponds to gain means 144 for the amplitude adjustment of the pulsesignal of frequency charge pump 118 of Z-1.

During high or low limiting CR-23 gurantees that switch Z-4-d is on,preventing "latch-up" of high pressure limiting means 160. Thus, highpressure limiting means resets automatically.

While in the foregoing specification embodiments of the invention havebeen set forth in considerable detail for purposes of making a completedisclosure of the invention, it will be apparent to those skilled in theart that numerous changes may be made in such details without departingfrom the spirit and principles of the invention.

What is claimed is:
 1. A liquid chromatograhy pump comprising:a. piston,at least a portion of which is reciprocative within a chamber having afluid inlet and a fluid outlet, said piston having a first end portionand a second end portion, said first end portion contacting the fluid,said piston being capable of filling and emptying said chamber; b.motive means for reciprocating said piston within said chamber at aselected substantially constant speed, said substantially constant speeddetermined by constant speed setting means for fixing said motive meansat a substantially constant speed, said motive means contacting saidsecond end portion of said piston; c. valve means for permitting thefilling and emptying of said chamber coordinated with the pressureexerted by said piston within said chamber, said piston, motive means,and valve means cooperating to produce a fluid flow during a particulartime period, from said piston chamber relative to said selectedsubstantially constant speed; d. control means for changing the speed ofsaid motive means at a preselected portion of the time period of saidreciprocation of said piston within said chamber, said control meansincluding means for changing the speed of said motive means at thetermination of the chamber emptying stroke of said piston, and returningsaid motive means to said predetermined constant speed after a certaindistance of travel of said piston during its subsequent emptying stroke,said motive means speed changing means including pressure measuringmeans for measuring and signaling the pressure at said piston chamber;and detection means for detecting and signaling the termination of saidchamber emptying stroke of said piston, said motive means speed changingmeans activated upon receipt of said chamber emptying stroke terminationsignal from said detection means, said motive means returning to saidsubstantially constant speed upon receipt of said pressure signal fromsaid pressure measuring means.
 2. The liquid chromatographic pump ofclaim 1 in which said pressure measuring means comprises a pressuretransducer communicating with said piston chamber.
 3. A liquidchromatography pump for delivering fluid against a back pressurecomprising:a. piston, at least a portion of which is reciprocativewithin a chamber having a fluid inlet and fluid outlet said pistonhaving a first end portion and a second end portion, said first endportion contacting the fluid, said piston being capable of filling andemptying said chamber; b. motive means for reciprocating said pistonwithin said chamber at a selected substantially constant speed, saidsubstantially constant speed determined by constant speed setting meansfor setting said motive means at a substantially constant speed, saidmotive means contacting said second end portion of said piston; c. valvemeans for permitting and filling and emptying of said chambercoordinated with the pressure exerted by said piston within saidchamber; said piston, motive means and valve means cooperating toproduce a time duration of fluid flow from said chamber relative to saidselected substantially constant speed; d. control means for changing thespeed of said motive means at a preselected portion of the time periodof said reciprocation of said piston within said chamber, said controlmeans comprising detection means for signaling the inception andtermination of the emptying of said chamber by said piston; pressuremeasuring means for measuring and signaling the pressure at said pistonchamber; summing amplifier producing an error signal; integratorreceiving said error signal from said summing amplifier and a signalfrom ground, said summing amplifier and a signal from ground, saidsumming amplifier receiving as inputs said pressure signal and theoutput signal of said integrator, tachometer means producing a signalproportional to the speed of said motive means said constant speedsetting means producing a reference signal corresponding to a desiredspeed of said motive means; and servo summing amplifier, said errorsignal from said summing amplifier, said tachometer means signal andsaid normal speed setting means signal serving as inputs to said servosumming amplifier, said servo summing amplifier producing an amplifiederror signal to said motive means.
 4. The liquid chromatographic pump ofclaim 3 in which said pressure measuring means comprises a pressuretransducer communicating with said piston chamber. .Iadd.
 5. A fluidpump mechanism for delivering fluid against a back pressure comprising:apiston movable within a chamber for drawing fluid into the chamberduring a chamber filling interval, pressurizing the fluid during apressurizing interval and delivering the pressurized fluid from thechamber during a delivery interval of piston movement; means for movingthe piston at a predetermined rate during delivery of the pressurizedfluid; means including a pressure transducer communicating with thechamber for generating a signal having a value related to the pressureof fluid in the chamber; means for storing the value of the signalgenerated during a delivery interval; means for comparing a presentvalue of the signal during the chamber pressurizing interval with thestored value; and means for changing the rate of piston movement duringat least a portion of the chamber pressurizing interval to a rateexceeding the predetermined rate by an amount related to any differencebetween said present and stored values. .Iaddend..Iadd.
 6. The mechanismof claim 5 further including means for changing the rate of pistonmovement during the chamber filling interval to a rate exceeding thepredetermined rate. .Iaddend.